Bi-metal strip mounting



Filed May 11, 1953 HIGH ERATURE URE TROLE-D LOW TEMPERATURE 3; INVENTOR.

Mama; /Z a/-ma/7 ('04/65 United States Patent BI-METAL STRIP MOUNTINGJames Norman Coates, Grand Rapids, Mich. Application May 11, 1953,Serial No. 354,024 16 Claims. (Cl. 200138) This invention relates toimprovements in thermostatic switch and method of producing the same.The principal objects of the invention are:

First, to provide a novel thermostatic switch of the bimetal actuatedtype in which the bi-metal element is securely and permanently mountedin a support by having its end embedded in a supporting mass of materialthat is cast or molded in plastic condition around the element andhardened or set in place to secure the element.

Second, to provide a novel thermostatic switch having a fixed contactsupport and a movable bi-metal contact support fixedly secured in a castor molded mass that is hardened to hold the contact supports inpredetermined relative positions to open and close the contacts atpredetermined temperatures.

Third, to provide a thermostatic economically produced in determinedtemperature.

Fourth, to provide a method of producing thermostatic switches whichpermits the thermal characteristics of the switches to be predicted andaccurately controlled.

Fifth, to provide a method of producing thermally actuated switcheswhich permits switches to be made to open or close at predeterminedtemperatures.

Sixth, to provide a novel method of producing thermally actuatedswitches which produces a permanently stable switch at minimum cost.

Other objects and advantages of the invention will be apparent from aconsideration of the following description and claims. The drawings, ofwhich there is one sheet, illustrate several forms of the switch and thesteps in the method of producing it. No particular one of the formsillustrated is preferred as each form has advantages in dilferentsituations and uses.

Fig. 1 is an elevational view of a first form of the switch.

Fig. 2 is a bottom plan view of the switch in Fig. 1.

Fig. 3 is a cross sectional view along the line 3-3 in Fig. 2.

Fig, 4 is a cross sectional view along the line 44 in Fig. 3.

Fig. 5 is a longitudinal cross sectional view through the switch shownin Figs. 1 to 4 at an intermediate point in the process of itsmanufacture.

Fig. 6 is a cross sectional view of line 6-6 in Fig. 5.

Fig. 7 is a longitudinal cross sectional view through a second form ofthe switch.

Fig. 8 is a longitudinal cross sectional view through a third form ofthe switch in an intermediate point in a slightly modified method of itsassembly.

switch which can be quantity to operate at any pretaken along the planeFig. 9 is a perspective view of a fourth form of the switch.

Fig. 10 is a perspective view of a fifth form of the switch.

Fig. 11 is a schematic view illustrating several steps in the method ofproducing the switch.

Heretofore thermal switches of the bi-metal type have resorted toscrews, rivets or mechanical clamps of some sort to hold the fixed endof the bi-metal element in place. This is objectionable particularly inswitches that require an insulated mount for the bi-metal as theclamping means is liable to fracture the insulation or the insulationwill deteriorate in time and permit the clamp to loosen and thetemperature setting of the switch to drift. The present inventionovercomes these difiiculties and permits more accurate predeterminationof the operating temperature of the switch.

It is first pointed out that any given bi-metal element has definitepredictable deflection characteristics. That is, if one end is clampedor fixed, the free end will deflect a certain distance per unit lengthper degree of temperature change. The direction of deflection is also ofcourse known.

Starting from this point, the invention contemplates taking a bi-metalelement and an ordinary contact element or two bi-metal elements andtemporarily holding them in a predetermined relative position, either incontact closed or contact open position. Then pour or cast a fluid orplastic material in a mass around the fixed ends of the elements. Theelements and mass are then held at a fixed temperature until the masssolidifies and grips the elements in a permanent base. The base may bean integral or separable part of a more extensive mounting for theswitch.

If the temperature at which the mass of the base is solidified is thesame as the temperature corresponding to the operating position at whichthe terminal element are held temporarily, the elements will assume anunstressed position in the solidifying mass and the finished switch willbe automatically calibrated. That is, elements positioned in apredetermined position, either open or closed, at a predeterminedoperating temperature will remain in that position if the mass of thebase hardens at the same predetermined temperature. Once the base hasset or hard ened it may be further cured at higher tempreatures withoutdisplacing the contact elements from their calibrated positions.

For switches designed to operate at normal or atmospheric temperaturesor somewhat higher, the mass of base material consists of a syntheticresin or plastic material that has the property of setting or hardeningat the desired temperature. Such materials are known as cold settingcasting resins as distinguished from high temperature or pressuresetting plastics. When a high temperature switch is to be manufactured ahigh temperature setting plastic having a setting temperaturecorresponding to the switch temperature may be used.

A wide variety of cold setting resins or plastics are available. Theyusually include the resin proper and a catalyst that is mixed with theresin to start the hardening process. Usually, a filler such as silicaflour, is mixed with the resin to reduce shrinkage and produce a harderbase. The filler also reduces the amount and cost of the resin in eachswitch. The proportions and specific ingredients of the base can bevaried considerably but the following are examples of satisfactoryingredients.

A. Electrical embodiment resin #2 and hardener (catalyst) B or Cavailable from the Minnesota Mining and Manufacturing Company, inertfiller, 50% by weight of base.

B. Araldite resin D and associated catalyst available from Ciba Company,Incorporated, New York City, inert filler.

C. Polyform G and associated catalyst available from B. G. FormanCompany, New York City, inert filler.

These resins are in the epoxy group and sometimes referred to asethoxylines but it is pointed out that other resins or plastics havingthe desired property can be used. In fact where a single bi-metalelement is to co-act with an adjustable contact that can be insulatedfrom the bi-metal mount, a low melting point metal may be used as themass of the base.

The examples of the switch illustrated include in Figs. 1 to 6 an outertubular body 1 having upper and lower end caps 2 and 3. A gasket 4 inthe bottom of the body supports a fixed cantilever element 5 and abi-metal element *6. Terminal wires 7 attached to the contact elementsextend through holes in the gasket and lower cap and temporarily locatethe lower ends of the elements 5 and 6.

In assembly of the switch a temporary spacer disc 8 is inserted in thebody 1. The disc has a hole 9 that receives the upper ends of thecontact elements and holds them in contact. The mass of resin that formsthe base Jill is introduced in fluid or plastic form either before orafter the disc as by pouring the resin through the hole 9. The switch isthen held at a temperature corresponding to the desired switch closingtemperature until the base material sets after which the disc 8 isremoved. The switch or its base material can then be further cured athigher temperature and the end caps installed.

The switch shown in Fig. 7 includes a tubular body 12 that may be ofeither metallic or electrically insulating material. A gasket 13 in thebottom of the body initially supports a single bi-metal element 14having a contact point 15. The contact point 15 coacts with anadjustably fixed contact point or screw 15. If the body 12 is metal andmust be insulated from the bi-metal, a grommet 17 is provided in thewall of the body. The base 18 is molded in the body and around theelement 14.

Since the contact 16 is adjustable, less care is required in positioningthe element 14. The material of the base 18 may be hardened at anytemperature and may even consist of a low melting point metal.

The switch shown in Fig. 8 includes two bi-metal elements l9 and 29. Thelower ends of the elements 19 and Zil are located by a gasket 21 in thebody 22 and a spacer 23 locates the points of the contact elements inspaced relationship. The base 24 is molded around the ends of elements19 and by inverting the body and pouring the base forming materialtherein. The base material is hardened as in the case of the switch inFigs. 1 to 6 at a predetermined temperature so that when the spacer 23is removed the bi-metal elements will assume the position illustratedwhenever the temperature of the switch approximates the temperature atwhich the base material was cured or set.

The switch in Fig. 9 substitutes a channel shaped body 25 for thepreviously described tubular bodies. The bimetal element 2s is securedin a molded base 27 that may be either cold setting resin or achemically setting material such as Portland cement or plaster of Parisor the base may be of molded or cast metal. The contact point 23 isadjustable.

The switch shown in Fig. 10 is similar to that shown in Figs. 1 to 6except that a separate reusable mold is used to receive the sleeve 29and base 34). This switch in Fig. 10 is adapted to be mounted in anysuitable mounting or holder.

Fig. 11 shows conventionally the method of producing the switches. Theswitches are mounted in a suitable mold or holder 31 and thebasematerial poured as at 32. The switches are then hardened atpredetermined controlled temperature at 33 and may be further cured athigher temperature at 34.

It should be pointed out that most cold setting resins and chemicallysetting materials harden in an exotherm process that develops some heatin the bi-metal elements embedded therein. This exothermic heat must betaken into account in determining the initial setting temperaturemaintained at 33. Depending on the quantity of the mass in each base andthe heat developed thereby, the setting temperature maintained at 33 maybe 4 several degrees lower than the temperature at which the switch isdesigned to operate.

For the purpose of this disclosure and appended claims, the termchemically setting plastic material is defined as any material orcombination of materials that will chan e from a liquid or semi-liquidstate at various temperatures to a solid state as a result of chemicalreaction and without recourse to heating or cooling the material to anyparticular temperature.

Having thus described my invention, what I claim as new desire to secureby Letters Patent is:

l. A thermostatic switch comprising, an elongated tubular body, a gasketof insulating material in one end of said body, a pair of elongatedcontact elements positioned in said body and seated against said gasket,lead wires secured to said elements and projecting through said gasketand located thereby, and a base comprising a mass of chemically settingresin molded and solidified in place Within said body and against saidgasket and arouin the ends of said elements, one of said elements beinga bi-metal element, said resin having the property of solidifying at thetemperature at which the switch operates.

2. A thermostatic switch comprising, an elongated body, a gasket ofinsulating material in one end of said body, a pair of elongated contactelements positioned in said body, lead wires secured to said elementsand projecting through said gasket and located thereby, and a basecomprising a mass of chemically setting resin molded and solidified inplace within said body and against said gasket and around the ends ofsaid elements, one of said elements being a bi-metal element, said resinhaving the property of solidifying at the temperature at which theswitch operates.

3. A thermostatic switch comprising, an elongated tubular body, a pairof elongated contact elements positioned in said body, lead wiressecured to said elements and projecting from the end of said body, and abase comprising a mass of chemically setting electrically insulatingmaterial and an inert filler molded and solidified in place Within saidbody and around the ends of said elements, one of said elements being abi-metal element, said insulating material having the property ofsolidifying at the temperature at which said switch operates.

. 4. A thermostatic switch comprising, an elongated body, a pair ofelongated contact elements positioned in said body, and a basecomprising a mass of chemically setting electrically insulating materialand an inert filler molded and solidified in place within said body andaround the ends of said elements, one of said elements being a bi-metalelement, said insulating material having the property of solidifying atthe temperature at which said switch operates.

5. A thermostatic switch comprising a pair of elongated coacting contactelements, lead wires secured to said clements and projecting therefrom,and a base comprising a mass of chemically setting electricallyinsulating material and an inert filler molded and solidified in placearound the ends of said elements, one of said elements being a bi-metalelement, said insulating material having the property of solidifying atthe temperature at which said switch operates.

6. A thermostatic switch comprising a pair of elongated coacting contactelements, and a base comprising a mass of chemically settingelectrically and insulating material molded and solidified in placearound the ends of said elements, one of said elements being a bi-metalelement, said insulating material having the property of soliditying atthe temperature at which said switch operates.

7. A thermostatic switch comprising a bi-metal contact elements havingone end molded and secured in a mass of chemically setting material,said material having the property and ability to solidify at theoperating temperature of the switch.

8. A thermostatic switch comprising, an elongated body, an elongatedcontact element positioned in said body, a lead wire secured to saidelement and projecting from said body, a second contact elementadjustably mounted on said body to coact with one end of said firstelement, and a base comprising a mass of chemically setting materialmolded and solidified in place within said body and around the other endof said first element, said first element being a bi-metal element andbeing insulated from said second element, said material having theproperty of solidifying at the temperature at which the switch operates.

9. A thermostatic switch comprising, an elongated body, an elongatedcontact element positioned in said body, a second contact elementadjustably mounted on said body to coact with one end of said firstelement, and a base comprising a mass of material molded and solidifiedin place within said body and around the other end of said firstelement, said first element being a bi-metal element and being insulatedfrom said second element, said material having the property ofsolidifying at the temperature at which the switch operates.

10. The method of producing a thermostatic switch which comprises thesteps of, placing a pair of contact elements including a bi-metalelement in predetermined coacting relationship in a body with theircontact points in contact, molding a base of chemically setting materialaround the opposite ends of said elements from their points while thematerial is plastic in character, subjecting elements and base to apredetermined temperature corresponding to the designed operatingtemperature of the switch until the material hardens and while theelements are held in said predetermined position, and thereafterreleasing the free ends of said elements and curing said base at ahigher temperature.

11. The method of producing a thermostatic switch which comprises thesteps of, placing a pair of contact elements including a bi-metalelement in predetermined coacting relationship in a body, molding a baseof chemically setting material around the opposite ends of said elementsfrom their points while the material is plastic in character, subjectingelements and base to a predetermined temperature corresponding to thedesigned operating temperature of the switch until the material hardensand while the elements are held in said predetermined position, andthereafter releasing the free ends of said elements.

12. The method of producing a thermostatic switch which comprises thesteps of, placing a pair of contact elements including a bi-metalelement in predetermined coacting relationship in a body with theircontact points out of contact, molding a base of chemically settingmaterial and an inert filler around the opposite ends of said elementsfrom their points While the material is plastic in character, subjectingelements and base to a predetermined temperature corresponding to thedesigned operating temperature of the switch until the material hardensand while the elements are held in said predetermined position, andthereafter releasing the free ends of said elements and curing said baseat a higher temperature.

13. The method of producing a thermostatic switch which comprises thesteps of, placing a pair of contact elements including a bi-metalelement in predetermined coacting relationship in a body, molding a baseof chemisally setting material and an inert filler around the oppositeends of said elements from their points while the material is plastic incharacter, subjecting elements and base to a predetermined temperaturecorresponding to the designed operating temperature of the switch untilthe material hardens and while the elements are held in saidpredetermined position, and thereafter releasing the free ends of saidelements.

14. The method of producing a thermostatic switch which comprises thesteps of, placing a bimetal contact element with its contact point inpredetermined coacting relationship with a fixed contact point and itssupport, molding a base of chemically setting material around theopposite end of said bimetal element from its point and between saidbimetal element and the support for said fixed contact point, andholding the structure thus assembled at a predetermined temperaturecorresponding to the operating temperature of the switch while thematerial of said base hardens and while holding said points in saidpredetermined position whereby said bimetal element assumes a shapecorresponding to said temperature and is held by the hardened base insaid predetermined position.

15. The method of producing a thermostatic switch which comprises thesteps of, placing a bimetal contact element with its contact point inpredetermined coacting relationship with a fixed contact point and itssupport, molding a base of chemically setting material around theopposite end of said bimetal element from its point and between saidbimetal element and the support for said fixed contact point, holdingthe structure thus assembled at a predetermined temperaturecorresponding to the predetermined position of said points, and causingthe material of said base to harden while holding said points and saidtemperature whereby the embedded end of said bimetal elment assumes aposition corresponding to said temperature and is held by the hardenedbase in said predetermined position.

16. The method of producing a thermostatic switch which comprises thesteps of, placing a bi-metal contact element with its contact point inpredetermined coacting relationship with a support for a fixed contactpoint, molding a base of chemically setting material around the oppositeend of said bi-metal element from its point and between said bi-metalelement and said support for the fixed contact point, holding thestructure thus assembled at a predetermined temperature corresponding tothe predetermined position of said point, and causing the material ofsaid base to harden while holding said point and said temperaturewhereby the embedded end of said bi-metal elment assumes a positioncorresponding to said temperature and is held by the hardened base insaid predetermined position.

References Cited in the file of this patent UNITED STATES PATENTS1,161,193 Cook Nov. 23, 1915 1,837,142 Bailey Dec. 15, 1931 2,060,774Zurcher Nov. 10, 1936 2,320,811 Cook June 1, 1943 2,559,141 WilliamsJuly 3, 1951 2,623,137 Vogelsberg Dec. 23, 1952

1. A THERMOSTATIC SWITCH COMPRISING, AN ELONGATED TUBULAR BODY, A GASKETOF INSULATING MATERIAL IN ONE END OF SAID BODY, A PAIR OF ELONGATEDCONTACT ELEMENTS POSITIONED IN SAID BODY AND SEATED AGAINST SAID GASKET,LEAD WIRES SECURED TO SAID ELEMENTS AND PROJECTING THROUGH SAID GASKETAND LOCATED THEREBY, AND A BASE COMPRISING A MASS OF CHEMICALLY SETTINGRESIN MOLDED AND SOLIDIFIED IN PLACE WITHIN SAID BODY AND AGAINST SAIDGASKET AND AROUND THE ENDS OF SAID ELEMENTS, ONE OF SAID ELEMENTS BEINGA BI-METAL ELEMENT, SAID RESIN HAVING THE PROPERTY OF SOLIDIFYING AT THETEMPERATURE AT WHICH THE SWITCH OPERATES.